import jsPDF from "jspdf";
import html2canvas from "html2canvas";

/*
 * 使用说明
 * ele:需要导出pdf的容器元素(dom节点 不是id)
 * pdfFileName: 导出文件的名字 通过调用outPutPdfFn方法也可传参数改变
 * splitClassName: 避免分段截断的类名 当pdf有多页时需要传入此参数 , 避免pdf分页时截断元素  如表格<tr class="itemClass"></tr>
 * 调用方式 先 let pdf = new PdfLoader(ele, 'pdf' ,'itemClass');
 * 若想改变pdf名称 pdf.outPutPdfFn(fileName);  outPutPdfFn方法返回一个promise 可以使用then方法处理pdf生成后的逻辑
 * */
class PdfLoader {
  constructor(ele, pdfFileName, splitClassName) {
    this.ele = ele;
    this.pdfFileName = pdfFileName;
    this.splitClassName = splitClassName || "";
    this.A4_WIDTH = 841.89;
    this.A4_HEIGHT = 595.28;
  }

  async getPDF(resolve) {
    const ele = this.ele;
    const pdfFileName = this.pdfFileName;
    const eleW = ele.offsetWidth; // 获得该容器的宽
    const eleH = ele.scrollHeight; // 获得该容器的高
    const eleOffsetTop = ele.offsetTop; // 获得该容器到文档顶部的距离
    const eleOffsetLeft = ele.offsetLeft; // 获得该容器到文档最左的距离
    window.pageYoffset = 0;
    document.documentElement.scrollTop = 0;
    document.body.scrollTop = 0;
    const canvas = document.createElement("canvas");
    let abs = 0;
    const win_in =
      document.documentElement.clientWidth || document.body.clientWidth; // 获得当前可视窗口的宽度（不包含滚动条）
    const win_out = window.innerWidth; // 获得当前窗口的宽度（包含滚动条）
    if (win_out > win_in) {
      abs = (win_out - win_in) / 2; // 获得滚动条宽度的一半
    }
    canvas.width = eleW * 2; // 将画布宽&&高放大两倍
    canvas.height = eleH * 2;
    const context = canvas.getContext("2d");
    context.scale(2, 2); // 增强图片清晰度
    context.translate(-eleOffsetLeft - abs, -eleOffsetTop);
    ele.style.height = ele.scrollHeight + "px"; // 获取元素的滚动高度，用于截取被滚动条隐藏的部分
    html2canvas(ele, {
      backgroundColor: null,
      allowTaint: false,
      dpi: window.devicePixelRatio * 4,
      width: ele.width,
      height: ele.width,
      windowWidth: ele.scrollWidth,
      scale: 4, // 按比例增加分辨率
      useCORS: true, // 允许canvas画布内可以跨域请求外部链接图片, 允许跨域请求。
    }).then(async (canvas) => {
      const contentWidth = canvas.width;
      const contentHeight = canvas.height;
      ele.style.height = ele.clientHeight + "px"; // 获取元素的实际高度，不包括滚动条隐藏的部分
      // 一页pdf显示html页面生成的canvas高度;
      const pageHeight = (contentWidth / this.A4_WIDTH) * this.A4_HEIGHT; // 这样写的目的在于保持宽高比例一致 pageHeight/canvas.width = a4纸高度/a4纸宽度// 宽度和canvas.width保持一致
      // 未生成pdf的html页面高度
      let leftHeight = contentHeight;
      // 页面偏移
      let position = 0;
      // a4纸的尺寸[595,842],单位像素，html页面生成的canvas在pdf中图片的宽高
      const imgWidth = this.A4_WIDTH - 10; // -10为了页面有右边距
      const imgHeight = (this.A4_WIDTH / contentWidth) * contentHeight;
      const pageData = canvas.toDataURL("image/jpeg", 1.0);
      const pdf = jsPDF("l", "pt", "a4");
      // 有两个高度需要区分，一个是html页面的实际高度，和生成pdf的页面高度(841.89)
      // 当内容未超过pdf一页显示的范围，无需分页
      if (leftHeight < pageHeight) {
        // 在pdf.addImage(pageData, 'JPEG', 左，上，宽度，高度)设置在pdf中显示；
        pdf.addImage(pageData, "JPEG", 5, 0, imgWidth, imgHeight);
        // pdf.addImage(pageData, 'JPEG', 20, 40, imgWidth, imgHeight);
      } else {
        // 分页
        while (leftHeight > 0) {
          pdf.addImage(pageData, "JPEG", 5, position, imgWidth, imgHeight);
          leftHeight -= pageHeight;
          position -= this.A4_HEIGHT;
          // 避免添加空白页
          if (leftHeight > 0) {
            pdf.addPage();
          }
        }
      }
      pdf.save(pdfFileName + ".pdf", { returnPromise: true }).then(() => {
        // 去除添加的空div 防止页面混乱
        const doms = document.querySelectorAll(".emptyDiv");
        for (let i = 0; i < doms.length; i++) {
          doms[i].remove();
        }
      });
      this.ele.style.height = "";
      resolve();
    });
  }
  //此方法是防止（图表之类）内容因为A4纸张问题被截断
  async outPutPdfFn(pdfFileName) {
    return new Promise((resolve, reject) => {
      this.ele.style.height = "initial";
      pdfFileName ? (this.pdfFileName = pdfFileName) : null;
      const target = this.ele;
      const pageHeight = (target.scrollWidth / this.A4_WIDTH) * this.A4_HEIGHT;
      // 获取分割dom，此处为class类名为item的dom
      const domList = document.getElementsByClassName(this.splitClassName);
      // 进行分割操作，当dom内容已超出a4的高度，则将该dom前插入一个空dom，把他挤下去，分割
      let pageNum = 1; // pdf页数
      const eleBounding = this.ele.getBoundingClientRect();
      for (let i = 0; i < domList.length; i++) {
        const node = domList[i];
        const bound = node.getBoundingClientRect();
        const offset2Ele = bound.top - eleBounding.top;
        const currentPage = Math.ceil(
          (bound.bottom - eleBounding.top) / pageHeight
        ); // 当前元素应该在哪一页
        if (pageNum < currentPage) {
          pageNum++;
          const divParent = domList[i].parentNode; // 获取该div的父节点
          const newNode = document.createElement("div");
          newNode.className = "emptyDiv";
          newNode.style.background = "white";
          newNode.style.height =
            pageHeight * (pageNum - 1) - offset2Ele + 30 + "px"; // +30为了在换下一页时有顶部的边距
          newNode.style.width = "100%";
          divParent.insertBefore(newNode, node); //在每一个节点前面插入一个空的新节点，防止内容被分割截断
        }
      }
      // 异步函数，导出成功后处理交互
      this.getPDF(resolve, reject);
    });
  }
}

export default PdfLoader;
